A general turbine has a structure of cooling the turbine by using cooling air (a turbine cooling structure). Cooling air in the turbine contains a considerable amount dust (such as dust and rust). Therefore, in the turbine cooling structure, a filter is arranged on an upstream side of the turbine, thereby performing a reduction process of the dust in the cooling air by using the filter. With this structure, the inflow amount of dust to the turbine is reduced. As a conventional gas turbine employing such a structure, there has been known a technique described in Patent Literature 1.